The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
Moving Picture Experts Group (MPEG) and Video Coding Experts Group (VCEG) together stepped ahead of the existing MPEG-4 Part 2 and H.263 standard methods to develop a better and more excellent video compression technology. The new standard is called H.264/AVC (Advanced Video Coding) and was released simultaneously as MPEG-4 Part 10 AVC and ITU-T Recommendation H.264.
In the H.264/AVC standard, a residual signal is generated by performing an intra/inter prediction process in units of a macroblock having various types of subblocks, and encoding is performed after further reducing the number of bits by performing a transform/quantization process on the residual signal generated. In a conventional encoding method based on a macroblock, an encoder divides an input image in a 16×16 macroblock, generates a residual block by predicting each macroblock by a size of a sub-macroblock available according to an inter/intra mode, generates a frequency coefficient by applying integer transform designed based on 4×4 or 8×8 discrete cosine transform (DCT), to the residual block generated, and quantizes the frequency coefficient according to a predetermined quantization parameter (QP). In addition, a blocking effect caused by the transform/quantization process is reduced through loop filtering.
Loop filtering in H.264/AVC (deblocking filtering) is performed in units of a macroblock such as a 16×16 block, an 8×8 block, and a 4×4 block. The main purpose of loop filtering is to remove a blocking effect, and such a blocking effect is generated not in units of a macroblock but in unit of a transform. Since H.264/AVC performs loop filtering along boundaries of a 16×16 macroblock and 4×4 and 8×8 blocks, it is unsuitable for an M×N block size (M may be equal to N) and P×Q transform (P may be equal to Q) and has a problem of applying a filtering coefficient and depth (the number of pixels to be filtered) that is unsuitable for P×Q transform, to a filtering boundary. In addition, it has a problem of failing to variably apply a filtering strength and the number of pixels, as a block size and a transform size increase. Therefore, when various block sizes and transforms are used in high-quality video encoding/decoding technology to be developed in the future, a blocking effect cannot be effectively removed by loop filtering, thus leading to degradation of subjective/objective performance.